Detection of Spin Coherence in Cold Atoms via Faraday Rotation Fluctuations

TL;DR

This paper demonstrates a non-invasive method to detect spin coherence in cold atoms using Faraday rotation fluctuations, achieving significantly enhanced signal strength and providing insights into spin relaxation rates at ultracold temperatures.

Contribution

The study introduces a novel dispersive Faraday rotation fluctuation measurement technique for cold atoms, surpassing traditional spin noise spectroscopy in sensitivity and enabling detailed spin coherence analysis.

Findings

Achieved five orders of magnitude signal enhancement over traditional methods.

Measured spin relaxation rate of cold rubidium atoms at ultracold temperatures.

Observed significantly lower relaxation rates compared to thermal vapor.

Abstract

We report non-invasive detection of spin coherence in a collection of Raman-driven cold atoms using dispersive Faraday rotation fluctuation measurements, which opens up new possibilities of probing spin correlations in quantum gases and other similar systems. We demonstrate five orders of magnitude enhancement of the measured signal strength than the traditional spin noise spectroscopy with thermal atoms in equilibrium. Our observations are in good agreement with the comprehensive theoretical modeling of the driven atoms at various temperatures. The extracted spin relaxation rate of cold rubidium atoms with atom number density $\sim$10$^9/$cm$^3$ is of the order of 2$\pi\times$0.5 kHz at 150 $\mu$K, two orders of magnitude less than $\sim$ 2$\pi\times$50 kHz of a thermal atomic vapor with atom number density $\sim$10$^{12}/$cm$^3$ at 373 K.